The present invention relates to the field of implantable hearing aid devices, and more specifically to the sealing of implantable hearing aid componentry housings and interconnections therebetween. The invention is particularly apt for use in conjunction with implantable hearing aid actuator bellows.
Implantable hearing aid systems entail the subcutaneous positioning of various componentry on or within a patient""s skull, typically at locations proximal to the mastoid process. Such componentry typically includes a receiver for receiving transcutaneous RF and/or acoustic signals and an interconnected processor to provide processed signals. Additionally, some form of actuator is employed to utilize the processed signals to stimulate the ossicular chain and/or tympanic membrane within the middle ear of a patient.
By way of example, one type of implantable actuator comprises an electromechanical transducer having a vibratory member positioned to mechanically stimulate the ossicular chain via axial vibrations. (see e.g., U.S. Pat. No. 5,702,342). In another approach, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. Additional implantable componentry may include one or more power storage components and associated recharging componentry. Components of the above-noted nature may be utilized in either semi-implantable systems which utilize additional external mounted componentry (e.g. microphones and transmitters located in behind-the-ear units) and fully-implantable systems which do not employ external componentry during normal usage.
As may be appreciated, reliable operation of implanted hearing aid componentry is extremely important to the long term viability and widespread utilization of implanted hearing aid systems. Such reliability is key from the perspective of not only achieving ongoing enhanced hearing, but additionally due to the high costs associated with surgical procedures attendant to the servicing/repair of implanted components.
In conjunction with achieving high reliability, the need to isolate implanted componentry from bodily fluids has been recognized (see e.g. U.S. Pat. No. 5,282,858). While significant advances have been made to enclose implanted componentry in sealed housings, the present inventors have devised further improved techniques to realize enhanced sealing in implantable hearing aid systems. Such techniques include the capability to achieve reliable sealing while allowing for relative movement between mechanically interconnected hearing aid componentry. In the later regard, the inventive techniques are particularly well-suited for implementation in implanted hearing aid systems that include a bellows to facilitate axial vibration of a vibratory member of an electromechanical transducer actuator.
In view of the foregoing, a general objective of the present invention is to provide an implantable hearing aid apparatus with improved sealing, thereby yielding enhanced reliability.
A further objective of the present invention is to provide an improved implantable hearing aid while maintaining or even reducing overall mass and complexity.
Another objective of the present invention is to provide an improved implantable hearing aid that can be produced in a highly consistent manner.
Yet a further objective of the present invention is to provide an improved implantable hearing aid apparatus that accommodates relative movement between implanted housing members while enhancing the sealing therebetween.
In relation to realizing the above-identified objectives, the present inventors have recognized that significant advances are achievable through the utilization of electrodeposition techniques. Specifically, it has been recognized that electrodeposition may be advantageously utilized to both sealably interconnect implanted hearing aid componentry housing members and in the fabrication of multi-layered implanted hearing aid housing members.
Based on such recognition, and in one aspect of the present invention, an implantable hearing aid apparatus is provided that comprises first and second implantable hearing aid component housing members, and at least one electrodeposited layer overlapping adjacent portions of the first and second housing members to provide an interconnection and hermetic seal therebetween. Preferably, the outer electrodeposited layer may comprise a biocompatible first material, such as a biocompatible metal selected from a first metals group consisting of gold, platinum and titanium.
In conjunction with this inventive aspect, an outer electrodeposited layer and a conformal underlying electrodeposited layer may be provided, wherein the outer layer comprises a first material that is different than a second material comprising the underlying layer. Preferably, the outer layer hermetically seals the underlying layer. Further, the underlying layer may be provided to have at least one of a modulus of elasticity, tensile strength and yield strength that is at least two times greater than that of the electrodeposited outer layer. By way of primary example, the underlying electrodeposited layer may comprise a second material selected from a second metals group consisting of nickel, iron, chromium, platinum, iridium, copper and aluminum. Such an arrangement may be of benefit where a degree of relative movement between the housing members is desired.
In addition to an outer layer and underlying layer, a conformal inner electrodeposited layer may also be provided to hermetically seal the underlying layer between the outer layer and inner layer. As with the outer layer, the inner layer may comprise a biocompatible metal selected from the noted first metals group.
Of note, the first and second housing members may be advantageously configured to define a substantially flush interface region therebetween. Further, the electrodeposited layers(s) overlapping the interface region may be provided to be substantially, continuously arcuate and/or flat. By way of example, opposing ends of tubular first and second cylindrical housing members may be disposed in abutting relation, wherein one or more electrodeposited layer(s) is disposed across and about the abutting ends of the first and second housing members.
In one embodiment, one of the first and second housing members may be in the form of a hollow bellows employed in an electromechanical transducer actuator with a vibratory member extending therethrough. The hollow bellows may comprise a plurality of undulations which allow the bellows to respond in an accordion-like fashion to axial vibrations imparted to one end thereof (e.g. via mechanical interconnection with the vibratory member). In such embodiment, the other one of the first and second housing members may be in the form of a sleeve member that is interconnected to one of an electromechanical transducer housing or to a distal end of the vibratory member that extends from the electromechanical transducer housing and through the hollow bellows and other housing member. Such sleeve member may advantageously comprise a biocompatible metal selected from the noted first metals group.
In another aspect of the present invention, an improved implantable hearing aid apparatus is provided that comprises first and second implantable hearing aid component housing members and a third implantable hearing aid component housing member interconnected therebetween. Specifically, the third housing member may be connected at a proximal end to the first housing member and at a distal end to the second housing member. Of importance, the third housing member may advantageously comprise a plurality of electrodeposited layers, wherein at least two adjacent ones of the plurality of electrodeposited layers comprise differing materials.
Preferably, an outer electrodeposited layer of the third housing member comprises a biocompatible material which substantially covers and thereby hermetically seals an underlying layer. Again, the underlying layer may be advantageously provided to have at least one of a modulus of elasticity, yield strength and tensile strength that is at least two times greater than that of the outer layer. By way of primary example, the outer layer may comprise a biocompatible metal selected from the first metals group identified above, and the underlying layer may comprise a metal selected from the second metals group noted above. The described, arrangement allows for relative axial movement of between the proximally/distally disposed first housing member/second housing member, respectively, while also yielding a reliably sealed structure.
In addition to the outer layer and underlying layer, an inner electrodeposited layer may also be provided to substantially cover and thereby hermetically seal the underlying layer. Preferably, the inner layer may comprise a biocompatible metal selected from the first metals group. As may be appreciated, the provision of a biocompatible inner layer that seals the underlying layer serves to preserve the functional integrity of the underlying layer in the event of bodily fluid leakage into the third housing member.
In conjunction with this inventive aspect, one or both of the first and second housing members, and the third housing member, may be configured to define a substantially flush interface region between adjacent portions thereof. Relatedly, at least one electrodeposited layer may be disposed in overlapping relation across the interface regions. By way of primary example, one end of each of the first and second housing members may be cylindrically configured to conformally abut opposing cylindrical ends of the third housing member, wherein biocompatible electrodeposited layers are disposed in a substantially continuous and arcuate manner over each of the two interface regions.
In one embodiment the third housing member may be in the form of a hollow bellows employed in an electromechanical transducer actuator with a vibratory member extending therethrough. The hollow bellows may comprise a plurality of undulations which allow the bellows to respond in an accordion-like fashion to axial vibrations imparted to one end thereof. More particularly, the proximal end of the bellows may be interconnected to (e.g. rigidly anchored) to an electromechanical transducer housing via a first housing member in the form of a tubular sleeve. The distal end of the bellows may be interconnected (e.g. rigidly) to the distal end of the vibratory member via a second housing member in the form of a tubular sleeve, wherein the vibratory member extends through all three housing members from the electromechanical transducer housing to communicate axial vibrations (e.g. to the ossicular chain within a patient""s middle ear).
In view of the foregoing, it will be appreciated that an inventive method is also provided for use in the manufacture of implantable hearing aid apparatus. In one aspect, the inventive method includes the steps of positioning first and second implantable hearing aid component housing members in adjacent relation, and electrodepositing at least a first layer of a first material on adjacent portions of the first and second housing members to establish an interconnection and hermetic seal therebetween. The method may further provide for the electrodeposition of a second layer of a second material on the first layer, wherein the first and second materials are different. Additionally, a third electrodeposited layer may be disposed on the second layer.
Where a single layer is utilized to provide a hermetical seal and interconnection between the first and second implantable hearing aid component housing members, it is preferable for such layer to comprise a biocompatible metal selected from the noted first metals group. Where two electrodeposited layers of differing materials are utilized, the underlying layer may have at least one of a modulus of elasticity, tensile strength and yield strength that is at least two times greater than that of the outer layer. Again, the underlying layer may comprise a metal selected from the second metals group.
In another aspect of the inventive method a first implantable hearing aid component housing member may be formed by electrodepositing at least a first layer of a first material onto a supporting shaped mandrel, and by selectively removing the shaped mandrel from within the shaped first layer. As may be appreciated the shaped first layer may integrally define an internal space. For such purposes, the shaped mandrel may be of a hollow configuration. In turn, the removing step may be advantageously completed by contacting the shaped mandrel with a removal fluid (e.g. so that the mandrel material may be flowed away with the fluid), thereby facilitating the formation of complex housing configurations. In this regard, the removing step may comprise one of chemically removing, dissolving and melting the shaped mandrel away from the shaped first layer, e.g. by flowing the removal fluid through the hollow shaped mandrel.
More particularly, the removal fluid may be an appropriate reagent for leaching the shaped mandrel off of the shaped first layer. For such purposes, the electrodeposited first material comprising the first layer should be chemically inert to the removal fluid. In one example, the shaped mandrel may comprise aluminum, and the reagent may comprise sodium hydroxide.
Alternatively, the removal fluid may comprise a solvent for selectively dissolving the shaped mandrel apart from the shaped first layer. For example, the mandrel may comprise an electrically conductive plastic composite and the solvent may comprise tetraethylene.
In another option, the shaped mandrel may comprise a low-melting point metal, such as iridium. The shaped mandrel may be heated above its melting point and removed from the first shaped layer via a removal fluid that is flowed thereby.
In conjunction with this aspect of the inventive method, a second layer of a second material may also be electrodeposited on the first layer in the formation of the first housing member, wherein the first and second materials are different. Further, a third layer (e.g. comprising a first material) may be electrodeposited on to the second layer in the formation of the first housing member.
As may be appreciated, the first material may comprise a metal selected from the above-noted first metals group, while the second electrodeposited layer may comprise a material selected from the above-noted second metals group. Such an arrangement facilitates the above-noted sealing and relative movement functionalities. Preferably, the first, second, and third layers may be sequentially electrodeposited over the shaped mandrel prior to selective removal of the supporting shaped mandrel.
The inventive method may further provide for the positioning of a second implantable hearing aid component housing member in adjacent relation to one end of the first housing member, and the electrodeposition of at least one overlapping layer of a first material (e.g. selected from the above-noted first metals group) on abutting end portions of the first and second housing members to establish an interconnection and hermetic seal therebetween. Further, a third implantable hearing aid component housing member may be then positioned in adjacent relation to another end of the first housing member, wherein at least one overlapping layer of a first material (e.g. selected from the above-noted first metals group) is electrodeposited on abutting end portions of the first and third housing members to establish an interconnection and hermetic seal therebetween.
Preferably, a central portion of the first housing member, as well as the non-abutting end portions of the second and third housing members (i.e. not abutting the first housing member) may be covered prior to the electrodeposition of the noted overlapping layers. Further, the overlapping layers may be simultaneously formed prior to the selective removal of the shaped mandrel, wherein the second and third housing members each comprise a material(s) that is not subject to removal by a removal fluid.
In one embodiment, the inventive method may be employed in the manufacture of an implantable actuator arrangement having a bellows (e.g. comprising three electrodeposited layers) interconnected at a proximal end to an electromechanical transducer housing via a proximal tubular sleeve, wherein an electrodeposited layer overlaps the bellows and proximal sleeve. A distal end of the bellows is interconnected to a vibratory member (e.g. that extends from the transducer housing) via a distal tubular sleeve, wherein an electrodeposited layer overlaps the bellows and distal sleeve. Such an arrangement yields a highly reliable actuator.
In an additional aspect of the inventive method, one or more of the noted electrodeposited layers may be formed in a plurality of substeps, wherein the electrodeposition process is interrupted then restarted between each sub-step so as to affect a discontinuity in grain pattern formation and thereby reduce incidences of pore alignment. By way of example, such interruption and restarting may simply entail the application, discontinuance, and re-application of an electrical current to a metallic shaped mandrel in a submersion electrodeposition bath process. Additionally and/or alternatively, one or more of the above-noted electrodeposited layers may be established utilizing a pulsed current (e.g. as opposed to a direct current), wherein nucleation may occur between each pulse to reduce the likelihood of pore formation.
In yet a further related aspect of the inventive method, the above-noted, multi-layered first housing member may be subjected to hot isostatic pressing to improve the fatigue characteristics thereof. More particularly, the multi-layered first housing member may be subjected to an elevated temperature and pressure to enhance the microstructure of one or more of the electrodeposited layers. The temperature and pressure utilized should be selected so that the yield strength of the intended affected layer (e.g. the second of three layers) is less than the treatment pressure at the treatment temperature. HIP processing may also be utilized to treat the noted second and third housing members too.